CN114466721B - Resistance spot welding method and manufacturing method of resistance spot welding joint - Google Patents
Resistance spot welding method and manufacturing method of resistance spot welding joint Download PDFInfo
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- CN114466721B CN114466721B CN202080067653.5A CN202080067653A CN114466721B CN 114466721 B CN114466721 B CN 114466721B CN 202080067653 A CN202080067653 A CN 202080067653A CN 114466721 B CN114466721 B CN 114466721B
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- 238000000034 method Methods 0.000 title claims abstract description 53
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- 238000005304 joining Methods 0.000 claims abstract description 3
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- 229910052739 hydrogen Inorganic materials 0.000 claims description 30
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- 230000005611 electricity Effects 0.000 claims description 3
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- 239000011701 zinc Substances 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
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- 239000000155 melt Substances 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
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- 238000005275 alloying Methods 0.000 description 1
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- 230000015572 biosynthetic process Effects 0.000 description 1
- ZTXONRUJVYXVTJ-UHFFFAOYSA-N chromium copper Chemical compound [Cr][Cu][Cr] ZTXONRUJVYXVTJ-UHFFFAOYSA-N 0.000 description 1
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
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- 230000008018 melting Effects 0.000 description 1
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- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical compound OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
- B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/002—Resistance welding; Severing by resistance heating specially adapted for particular articles or work
- B23K11/0026—Welding of thin articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
- B23K11/163—Welding of coated materials
- B23K11/166—Welding of coated materials of galvanized or tinned materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/24—Electric supply or control circuits therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/006—Vehicles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/18—Sheet panels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/34—Coated articles, e.g. plated or painted; Surface treated articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
Abstract
The purpose is to provide a resistance spot welding method and a method for manufacturing a resistance spot welding joint. The present invention provides a resistance spot welding method for joining two or more steel sheets, which are stacked together as steel sheets to be welded, by sandwiching the steel sheets to be welded between a pair of electrodes, and by applying a current while pressurizing, wherein the two or more steel sheets include one or more steel sheets having a tensile strength of 980MPa or more, and the method comprises, as a current application: an initial power-on procedure, while meetingIs set at a pressure F of (2) 1 (kN) pressurizing while satisfyingCurrent value I of (2) 1 (kA) energizing; and a main energizing step of forming a nugget having a predetermined nugget diameter and generating spatter in the initial energizing step.
Description
Technical Field
The present invention relates to a resistance spot welding method and a method for manufacturing a resistance spot welding joint.
Background
Resistance spot welding is widely used for assembling a vehicle body such as an automobile, and resistance spot welding is performed at up to several thousand points on one vehicle body. In resistance spot welding, two or more steel plates are stacked together, and energized while being sandwiched and pressed by a pair of welding electrodes disposed on the upper and lower sides of the steel plates. Thus, nuggets of a predetermined size are formed at the joint portions of the steel plates, and the steel plates are joined to obtain a welded joint.
In recent years, from the viewpoint of environmental protection, reduction of CO of automobiles has been demanded 2 The discharge amount is reduced by using a high-strength steel plate for the vehicle body, thereby realizing the improvement of fuel efficiency, which is the weight reduction of the vehicle body. However, high-strength steel sheets generally contain not only a large amount of C but also various alloying elements to improve strength and increase hydrogen embrittlement sensitivity. In addition, in resistance spot welding, rust preventive oil, moisture, a coating layer, and the like on the surface of a steel sheet are involved in weld metal (molten portion) during melting and solidification at the time of welding, and remain after cooling as a hydrogen source, which is a factor of occurrence of delayed fracture.
Therefore, when high-strength steel sheets are welded by resistance spot welding, the occurrence of delayed fracture due to penetration of hydrogen into a weld metal having high hydrogen embrittlement sensitivity at the time of welding becomes a problem in the welded portion of the obtained welded joint.
As a method for preventing delayed fracture of a welded portion, the following patent documents are available. For example, patent document 1 discloses the following technique: by increasing the pressurizing force and decreasing the current immediately after the welding energization (main energization), the residual stress of the welded portion is controlled and delayed fracture is prevented. Further, for example, patent document 2 discloses the following technique: the structure and hardness of the welded portion are controlled and delayed fracture is prevented by increasing the pressurizing force immediately after the welding energization (main energization) and energizing after the cooling time without energization has elapsed.
Prior art literature
Patent literature
Patent document 1: japanese patent application laid-open No. 2015-93282
Patent document 2: international publication No. 2014/171495
Disclosure of Invention
Problems to be solved by the invention
As described above, in resistance spot welding of a high-strength steel sheet, there is a problem in that hydrogen intrudes into the weld metal. Therefore, in resistance spot welding of high-strength steel sheets, it is important to not only increase the strength of the welded joint but also reduce the amount of hydrogen remaining in the welded portion in order to prevent delayed fracture.
However, the techniques of patent document 1 and patent document 2 do not reduce the hydrogen amount at the welded portion in order to prevent delayed fracture. In addition, these techniques have the following problems: when the pressurizing force is excessively increased in a molten state immediately after the welding is energized, the plate thickness of the welded portion is liable to decrease, and the strength of the obtained welded joint is lowered or the appearance of the welded portion is impaired.
The problem of delayed fracture due to penetration of hydrogen into a weld metal having a high hydrogen embrittlement sensitivity during welding is not limited to the case of resistance spot welding of high-strength steel sheets for automobiles, but is also similarly present in resistance spot welding of other steel sheets.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a resistance spot welding method and a resistance spot welding joint manufacturing method capable of stably forming a nugget having a large diameter while suppressing delayed fracture of a welded portion.
Means for solving the problems
The inventors of the present invention examined the behavior of hydrogen that intruded into the weld metal at the time of welding, which is a factor of delayed fracture, in order to suppress delayed fracture of a welded joint obtained by resistance spot welding of a high-strength steel sheet having a large tensile strength, and found the following findings.
As described above, first, hydrogen enters the welded portion during welding. Since diffusion of hydrogen becomes slower as the temperature is lowered, many hydrogen remains without diffusing from the inside of the nugget due to quenching after welding. Thereafter, hydrogen accumulates in a portion where a large tensile stress represented by the notch shape of the nugget end portion concentrates with the lapse of time, thereby generating delayed fracture.
Therefore, it is effective to remove more hydrogen from the nugget during welding and reduce the residual hydrogen amount to suppress delayed fracture.
Accordingly, the present inventors have intensively studied a preferable resistance spot welding condition capable of reducing the residual hydrogen amount of the welded portion. The results are described below.
In the power-on step, first, spatter is generated from the butt surface of the steel sheet, and thus the hydrogen source present on the butt surface of the steel sheet can be discharged as spatter. As a result, it was found that the incorporation of hydrogen into the nugget in the subsequent energizing step was reduced, and the delayed fracture resistance of the welded joint was improved. However, when spatter is generated at the later stage of the power-on process, it is difficult to reduce hydrogen mixed into the nugget before the spatter is generated. As a result, there are cases where delay damage cannot be suppressed, the growth of the nugget is affected, and a large nugget diameter cannot be ensured.
Thus, it can be seen that: the power-on process is divided into two stages, specifically, a first power-on process (initial power-on process described later) for generating spatter and a second power-on process (main power-on process described later) for forming a nugget, whereby spatter can be generated in the initial stage of the power-on process and the spatter can be suppressed in the later stage of the power-on process.
Further, by using the contact resistance of the steel plate butt surface at the initial stage of the energizing step, only the vicinity of the steel plate surface where the hydrogen source is located is selectively melted, and the minimum-necessary-scale splashing is generated. This can efficiently discharge hydrogen. Therefore, it is clear that control of the appropriate pressurizing force and current value in the first energization step (initial energization step) becomes important.
By providing the first current-carrying step (initial current-carrying step), the adhering matter such as moisture, oil, dirt, etc. existing on the abutting surface of the steel plates is discharged together with the splashes. As a result, the abutting surface of the steel sheet can be kept clean, and the steel sheet can be moderately softened before nugget formation by electric heating. From this, it can be seen that: the contact state between the steel plates can be maintained well, and the effect of improving the delayed fracture resistance can be obtained. It is also known that the effect of forming the nugget having a large nugget diameter more stably is obtained at the same time in the second power supply step (main power supply step).
The present invention has been made based on the above-described findings, and has the following gist.
[1] In a resistance spot welding method for joining two or more steel sheets, which are stacked together as steel sheets to be welded, by sandwiching the steel sheets to be welded between a pair of electrodes and applying electric current while pressurizing, the two or more steel sheets include one or more steel sheets having a tensile strength of 980MPa or more,
the energizing includes: an initial power-on step of applying a pressurizing force F satisfying the following formula (1) 1 (kN) A current value I satisfying the following formula (2) is used while pressurizing 1 (kA) energizing; and
a main power-on step of forming a nugget having a predetermined nugget diameter,
splash is generated in the initial energization process,
here, t 1 : total plate thickness (mm) of the welded steel plate.
[2] The method of resistance spot welding according to item [1], wherein the energization time in the initial energization step is 10ms or more and 200ms or less.
[3]In [1]]Or [2]]The resistance spot welding method further comprises a step of providing a current value I satisfying the following formula (3) between the initial energizing step and the final energizing step c (kA) an electric current-carrying cooling step,
0≤I c ≤I 1 …(3)
here, I c : the current value (kA) in the cooling step,
I 1 : current value (kA) in the initial energization step.
[4] The resistance spot welding method according to any one of [1] to [3], wherein a welding voltage Vs (V) at the time of generating the spatter satisfies the following formula (4),
Vs≥0.7×Va…(4)
here, va: the welding voltage (V) 5ms before the spatter generation,
vs: welding voltage (V) at the moment of spatter generation.
[5] A method for producing a resistance spot welding joint, wherein the resistance spot welding method according to any one of [1] to [4] is used.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, since a nugget having a large diameter can be stably formed while suppressing delayed fracture of a welded portion, an industrially excellent effect is obtained.
Drawings
Fig. 1 is a cross-sectional view schematically illustrating resistance spot welding according to an embodiment of the present invention.
Fig. 2 is a diagram illustrating an example of a welded joint used in the embodiment of the present invention, in which fig. 2 (a) is a plan view and fig. 2 (b) is a side view.
Detailed Description
The resistance spot welding method and the method for manufacturing a resistance spot welding joint according to the present invention will be described below with reference to the drawings. The present invention is not limited to this embodiment.
Initially, the resistance spot welding method of the present invention will be described with reference to fig. 1.
The invention joins two or more steel plates by resistance spot welding. Fig. 1 schematically illustrates an example of a resistance spot welding method. Fig. 1 shows an example of resistance spot welding performed on two steel plates.
First, two or more steel sheets are stacked. In the example shown in fig. 1, two steel sheets, that is, a steel sheet disposed on the lower side (hereinafter, also referred to as a lower steel sheet 1) and a steel sheet disposed on the upper side (hereinafter, also referred to as an upper steel sheet 2), are overlapped and used as steel sheets to be welded.
Next, the overlapped steel plates (the lower steel plate 1 and the upper steel plate 2) are sandwiched between a pair of welding electrodes (electrodes) 4, 5 arranged in the vertical direction of the overlapped steel plates, and energized in an energizing pattern (pattern) described later while being pressurized. In the example shown in fig. 1, the electrode disposed on the lower side of the steel plate is referred to as a lower electrode 4, and the electrode disposed on the upper side of the steel plate is referred to as an upper electrode 5.
In this way, the overlapped steel plates are pressed and energized while being sandwiched between the pair of welding electrodes 4 and 5, and the nugget 3 having a desired size is formed by resistance heat generation, and the overlapped steel plates are joined to each other, whereby a welded joint can be obtained. Although not shown, in the present invention, three or more steel sheets may be superimposed and resistance spot welded, and in this case, a welded joint can be obtained in the same manner as in the welding method described above.
The device for performing the resistance spot welding method of the present invention is not particularly limited as long as it is configured to be capable of pressurizing by the lower electrode 4 and the upper electrode 5 and controlling the pressurizing force at will. For example, conventionally known devices such as a cylinder and a servo motor can be used. The configuration for supplying current and controlling the current value at the time of energization is not particularly limited, and conventionally known devices can be used. The present invention can be applied to either direct current or alternating current. In the case of ac, "current" means "effective current".
The form of the tips of the lower electrode 4 and the upper electrode 5 is not particularly limited. For example, JIS C9304: DR (dome radius), R (radius shape), D (dome shape), etc. described in 1999. The diameters of the tips of the lower electrode 4 and the upper electrode 5 are, for example, 4mm to 16mm. The resistance spot welding was performed in a state where the electrode was always water-cooled.
In the present invention, the steel grade of the resistance spot welded steel sheet is not particularly limited. At least one of the superimposed steel sheets is a high-strength steel sheet having a tensile strength of 980MPa or more. This is because delayed fracture of the resistance spot welding portion is particularly problematic in high-strength steel sheets having a tensile strength of 980MPa or more, and the effects of the present invention can be obtained more effectively.
The thickness of the resistance spot welded steel sheet is not particularly limited. For example, the diameter is preferably in the range of 0.5mm to 3.0 mm. This is because a steel sheet having a sheet thickness within this range can be suitably used as an automobile member.
The resistance spot welded steel sheet may be a steel sheet that is subjected to a plating process and has a plating layer on the surface. In the present invention, examples of the plating include Zn-based plating and Al-based plating. Examples of the Zn plating include hot dip Galvanizing (GI), zn-Ni plating, and Zn-Al plating. Examples of the Al plating include al—si plating (e.g., al—si plating containing 10 to 20 mass% of Si). The melt plating layer may be an alloyed melt plating layer. Examples of the alloyed hot-dip coating layer include an alloyed hot-dip zinc (GA) layer.
Further, two or more steel sheets may be the same or different. That is, the steel plates may be the same type and shape, or may be different types or shapes. The surface-treated steel sheet having the plating layer and the steel sheet without the plating layer may be overlapped.
Next, the energization pattern in the resistance spot welding method according to the present invention will be described.
The present invention is a resistance spot welding method in which two or more steel sheets including one or more steel sheets having a tensile strength of 980MPa or more are overlapped to form a steel sheet to be welded, the steel sheet to be welded is sandwiched between a pair of electrodes, a nugget is formed by applying pressure and applying electricity, and the overlapped steel sheets (steel sheet to be welded) are joined. In the example shown in fig. 1, the steel sheets 1 and 2 sandwiched between the lower electrode 4 and the upper electrode 5 are energized in a specific pattern while being pressurized. The current application of the present invention includes an initial current application step and a main current application step for forming a nugget having a predetermined nugget diameter.
First, in the initial power-on step, the pressurizing force F satisfying the following formula (1) is applied at one side 1 (kN) while pressurizing, the current value I satisfying the following formula (2) 1 (kA) the energization is controlled so that a splash (splash) is generated in the initial energization step. That is, in the initial power-on step, the hydrogen source present on the butt surface of the steel plates is splashed and discharged, and a good contact state between the steel plates is ensured.
In the present invention, it is important to generate spatter in the initial power-on step. When the generation of the spatter is a step subsequent to the initial energization step (for example, a cooling step or a main energization step described later), a lot of hydrogen is mixed into the nugget before the spatter is generated. Therefore, it is difficult to obtain the hydrogen reducing effect by the splashing, and the delayed destruction suppressing effect cannot be obtained. In addition, when the effect of reducing hydrogen is to be more remarkably exhibited, it is effective to shorten the energization time before the splash generation and to minimize the mixing of hydrogen.
In the present invention, it is preferable that the splash is generated within 200ms from the start of the energization in the initial energization step. More preferably, the splash is generated within 100ms from the start of the energization of the initial energization step. The lower limit of the elapsed time from the start of the energization to the splash generation is not particularly limited, but is preferably 20ms or more.
In order to stably form a nugget having a large diameter in a main power-on step described later, it is preferable that the spatter generated in the initial power-on step is a small-scale spatter (hereinafter, may be referred to as a small spatter). When the voltage between the electrodes is measured in resistance spot welding, the resistance between the electrodes decreases when spatter is generated, and thus the measured value decreases in voltage. In the present invention, the size of the splash can be controlled according to the voltage drop amount at the time of the splash generation. Specifically, the current value and the pressurizing force in the initial energization step are preferably set so that the inter-electrode voltage (welding voltage) Vs (V) at the time of occurrence of spatter satisfies the following expression (4). The splash generated by energizing to satisfy the formula (4) means the small splash in the present invention.
Vs≥0.7×Va…(4)
Here, va: electrode voltage (welding voltage) (V) before 5ms of spatter generation, vs: the inter-electrode voltage (welding voltage) (V) at the time of spatter generation.
When the inter-electrode voltage Vs (V) at the time of occurrence of the spatter is smaller than (0.7×va), the scale of the spatter is large, and a good current-carrying state cannot be ensured in the main current-carrying process, so that a nugget having a large nugget diameter (hereinafter, also referred to as a diameter) cannot be stably formed. Therefore, the inter-electrode voltage Vs (V) at the time of generating the spatter is preferably set to (0.7×va) or more. In the case where it is desired to maintain the contact state between the steel plates well and to more remarkably exert the effect of stably forming nuggets having a large diameter in the main power-on step, it is effective to suppress the scale of the spatter as small as possible, and therefore it is more preferable to set the inter-electrode voltage Vs (V) at the time of occurrence of the spatter to (0.8×va) or more. In general, as described above, when spatter is generated during spot welding, the electrode voltage decreases. That is, since the inter-electrode voltage does not increase due to the occurrence of the spatter, it is considered that the above formula (4) does not exceed (1.0×va). Therefore, it is preferably smaller than (1.0 XVa).
After the initial power-on step, a main power-on step for forming a nugget having a predetermined diameter is performed. In the main power-on step, power-on conditions and pressurizing conditions such as a current value, a power-on time, and the like for forming the nugget are not particularly limited, and conventionally used welding conditions can be employed.
For example, from the viewpoint of forming a nugget of an appropriate diameter, the current value in the main conduction step is preferably 1.0kA or more and 15.0kA or less, and the pressurizing force in the main conduction step is preferably 1.0kN or more and 9.0kN or less. The energization time in the main energization step is preferably 100ms or more and 1000ms or less. The main energization step may be a multi-stage energization or a multi-stage pressurization step in which the current value and the pressurizing force are changed in the main energization step.
After the main power-on step, a holding step of holding the molten metal under pressure without power-on may be provided to cool the molten metal core. The holding time is not particularly specified, and is preferably 20 to 1000ms as a holding range in general resistance spot welding.
In the present invention, the nugget having a predetermined nugget diameter is preferably a nugget diameter of(t: plate thickness) (mm). When overlapping and welding steel plates having different plate thicknesses, the plate thickness of a steel plate having a smaller plate thickness out of two adjacent joined steel plates is set to t.
In the present invention, a cooling step described below may be further provided between the initial energization step and the main energization step.
Next, specific energization conditions for the initial energization step for realizing the resistance spot welding method of the present invention will be described.
In the initial power-on process, the pressurizing force F 1 (kN) and current value I 1 (kA) is set so as to satisfy the following formulas (1) and (2).
Here, t 1 : total plate thickness (mm) of the welded steel plate.
These conditions are conditions required for discharging the vicinity of the butt surface of the steel sheet melted by the contact resistance as splashes in the initial power-on step.
At a pressure F 1 (kN) isIn the following cases, the pressurizing force is too low to control the heat generation of the melt by the energization, and large splashing is extremely generated. As a result, it is difficult to stably form a large nugget in the subsequent main energization step. In addition, under the pressure F 1 (kN) exceeds->In the case of (2), it is difficult to discharge the portion melted by the contact resistance as splashes, and the effect of suppressing the delay damage cannot be obtained. In addition, although it is also possible to generate spatter by applying a high current, in this case, large spatter is extremely generated, and therefore it is difficult to stably form a large nugget in a subsequent main energization process.
At the current value I 1 (kA) isIn the following cases, it is difficult to generate spatter, and the effect of suppressing delay damage cannot be obtained. In addition, at the current value I 1 (kA) exceeds-> In this case, since large spatter is extremely generated, it is difficult to stably form a nugget having a large diameter in a subsequent main energization step. In the case where the effect of stably obtaining a nugget having a large diameter in the subsequent main energization step is to be more remarkably obtained while suppressing the delayed fracture, the pressurizing force F is preferable 1 (kN) and current value I 1 (kA) is set so as to satisfy the following formulas (5) and (6).
The initial energization step preferably sets the energization time to 10ms or more and 200ms or less. If the energization time is less than 10ms, the energization time is too short to stably generate spatter, and the effect of suppressing the delay damage cannot be stably obtained. In general, heat generation by a contact resistor occurs in an initial stage of energization. In the present invention, splash is generated in the heat generation stage using the contact resistance, and long-time energization after the splash generation causes not only an increase in useless time but also a large splash. For the above reasons, the energization time is preferably 200ms or less. Further, it is more preferable that the time period is 20ms or more and 140ms or less. More preferably, the time is 20ms or more and 100ms or less.
In the present invention, a current value I satisfying the following formula (3) may be set between the initial energization step and the main energization step c (kA) a cooling step of stabilizing the contact state between the steel plates by applying electricity.
0≤I c ≤I 1 …(3)
Here, I c : in the cooling processThe current value (kA),
I 1 : current value (kA) in the initial energization step.
By providing the cooling step, the contact state between the temporarily disturbed steel plates due to the occurrence of spatter can be stabilized again, and the effect of forming the nugget more stably in the subsequent main energization step can be obtained. Current value I in the cooling step c (kA) is a value exceeding the current value I in the initial energization step 1 When the value of (kA) is set, the possibility of occurrence of splash in the cooling step becomes high, and the effect of ensuring the contact state between the steel sheets may not be obtained. The purpose of this cooling step is to stabilize the contact state between the steel plates without generating spatter in the cooling step. Therefore, only the current value I in the cooling step c The energization mode of the cooling step is not particularly limited to the range satisfying the formula (3), and may be a no-energization step or a multi-stage energization step or a Down (Down) energization step in which no energization is performed. Current value I of cooling step c (kA) more preferably (0.5×I) 1 ) kA or less.
The time of the cooling step is preferably 500ms or less. When the energization is performed for a time exceeding 500ms in the cooling step, the total time of the welding step itself becomes long, and there is a possibility that productivity may be lowered. More preferably 300ms or less, and still more preferably 20ms or more.
Next, a method of manufacturing the resistance spot welding joint will be described.
The present invention is a method for manufacturing a resistance spot welding joint using the resistance spot welding method. In the method for manufacturing a resistance spot welding joint according to the present invention, for example, two or more steel sheets including one or more steel sheets having a tensile strength of 980MPa or more are stacked and sandwiched between a pair of welding electrodes, and resistance spot welding is performed while applying pressure and applying current to the welding conditions in the respective steps to form nuggets of a desired size, thereby obtaining a resistance spot welding joint. The steel sheet, the welding conditions, and the like are the same as those described above, and therefore, the description thereof is omitted.
As described above, according to the present invention, delayed fracture of the welded portion can be suppressed. Further, since the spatter having a small size satisfying the condition of the inter-electrode voltage is generated in the initial energization step, the nugget having a large diameter can be stably formed in the subsequent main energization step.
Further, according to the present invention, since penetration of hydrogen into a weld metal having high hydrogen embrittlement sensitivity can be effectively suppressed, the above-described effects can be obtained similarly in resistance spot welding of other steel sheets, not only in the case of resistance spot welding on a high-strength steel sheet for an automobile.
Examples
The operation and effects of the present invention will be described below with reference to examples. The present invention is not limited to the following examples.
In the embodiment of the present invention, as shown in fig. 1, the lower steel sheet 1 and the upper steel sheet 2 are overlapped and resistance spot welded. The resistance spot welding is performed at normal temperature, and the lower electrode 4 and the upper electrode 5 are always water-cooled. The lower electrode 4 and the upper electrode 5 were each a DR-shaped electrode made of chromium copper and having a diameter of the tip (tip diameter) of 6mm and a radius of curvature of 40 mm. In addition, the lower electrode 4 and the upper electrode 5 are driven by a servo motor to control the pressurizing force, and an ac power supply with a frequency of 50Hz is used at the time of energization.
The following three steels were used as the welded steel sheets.
[ Steel grade I ] A steel sheet having a tensile strength of 1470MPa, a long side of 100mm, a short side of 30mm and a sheet thickness of 1.0mm was not subjected to plating treatment.
[ Steel grade II ]]The tensile strength was 1470MPa, the long side was 100mm, the short side was 30mm, the sheet thickness was 1.6mm, and the sheet was subjected to a plating treatment (hot dip Galvanizing (GI) with an adhesion of 50g/m per one side 2 ) Is a steel plate.
[ Steel grade III]The tensile strength was 1320MPa, the long side was 100mm, the short side was 30mm, the sheet thickness was 2.0mm, and the sheet was subjected to a plating treatment (hot dip Galvanizing (GI) with an adhesion of 50g/m per one side 2 ) Is a steel plate.
Here, a welded joint used in the test will be described with reference to fig. 2 (a) and 2 (b).
Fig. 2 (a) is a top view of the welded joint, and fig. 2 (b) is a side view of the welded joint. At the time of resistance spot welding, as shown in fig. 2 (a) and 2 (b), a spacer 6 having a thickness of 1.6mm and a square of 30mm is sandwiched between two steel plates 1, 2 (the length in the long side direction is 100mm, and the length in the short side direction is 30 mm) of the steel grade, and temporary welding is performed. Next, the centers of the plate groups formed by overlapping two steel plates were welded using the conditions described in table 1. As shown in fig. 2 (a), temporary welding positions at both ends of the board group are designated as temporary welding points 8, and a welding position at the center of the board group is designated as a welding point 7.
In the welding, the diameter of the molten core becomes the diameter of the molten core under all conditionsThe current value was adjusted so as to be about (t: plate thickness (mm)) (mm). In the case of a steel sheet with a sheet thickness of 1.6mm, < > a->When welding steel plates with different plate thicknesses, the steel plate with a smaller plate thickness is used as a reference to be +.>The current value is adjusted in such a manner that the nugget diameter is increased.
The delayed fracture characteristics and the nugget stability were evaluated by the methods shown below.
The delay fracture characteristics were evaluated in the following manner.
In the delayed fracture test, the obtained welded joint was left to stand in the atmosphere at normal temperature (20 ℃) for 24 hours, and then the presence or absence of delayed fracture of the welded portion was examined. The welding was performed under the condition n=3, and in table 2, no delayed fracture occurred after standing for 24 hours, the mark "o" was recorded, and the delayed fracture occurred, the mark "x" was recorded.
Regarding the judgment of the delayed fracture characteristic, it was judged that delayed fracture occurred when detachment of nuggets (a phenomenon in which nuggets are detached into two at the joint interface) was visually observed after welding. As a final determination of the delay fracture characteristics, in table 2, a condition that three of n=3 do not cause delay fracture is described as "a (excellent)", and a condition that one or more of n=3 cause delay fracture is described as "B (not possible)".
Further, the test body was used to evaluate the stability of the nugget. The evaluation of the nugget stability was performed in the following manner.
After etching using a picric acid aqueous solution was performed on the cross section of the welded joint obtained by cutting the center of the welded portion, the length of the corroded nugget structure was measured, and the nugget diameter was calculated. The nugget diameter was calculated under the condition n=3, and in table 2, the nugget diameter wasThe symbol "∈is smaller than +.>The symbol "x" is described.
Regarding determination of nugget stability, in table 2, all n=3 are obtainedThe nugget diameter is described as "a (excellent)", and one or more of n=3 is smaller than +.>The conditions of the nugget diameter of (a) are described as "B (not possible)".
TABLE 1
TABLE 2
* A: preferably, B: is not possible
As is clear from table 2, in the present invention example, it is found that the effect of stably forming the nugget is obtained while suppressing the occurrence of delayed fracture in the welded joint.
Description of the reference numerals
1. Lower steel plate
2. Upper steel plate
3. Nugget
4. Lower electrode
5. Upper electrode
6. Spacer(s)
7. Welding point
8. Temporary welding point
Claims (4)
1. In a resistance spot welding method for joining two or more steel sheets, which are stacked together as steel sheets to be welded, by sandwiching the steel sheets to be welded between a pair of electrodes and applying electric current while pressurizing, the two or more steel sheets include one or more steel sheets having a tensile strength of 980MPa or more,
the energizing includes:
an initial energizing step of applying a pressurizing force F satisfying the following formula (1) at an energizing time of 20ms or more and 80ms or less 1 The current value I satisfying the following formula (2) is used while pressurizing 1 Electrifying; and
a main power-on step of forming a nugget having a predetermined nugget diameter,
in the initial energization step, splash is generated within 40ms from the start of energization to discharge the hydrogen source existing on the abutting surface of the steel plates,
here, t 1 : the total plate thickness of the welded steel plate,
the F is 1 Is in units of kN, I 1 Is in units of kA, t 1 Is in mm.
2. The resistance spot welding method according to claim 1, wherein,
the current value I satisfying the following formula (3) is also provided between the initial energization step and the main energization step c A cooling step of supplying electricity to the electric power,
0≤I c ≤I 1 …(3)
here, I c : the value of the current in the cooling process,
I 1 : the current value in the initial energization process,
the I is c 、I 1 Is in units of kA.
3. The resistance spot welding method according to claim 1 or 2, wherein,
the welding voltage Vs at the time of the spatter generation satisfies the following expression (4),
Vs≥0.7×Va…(4)
here, va: the welding voltage 5ms before the spatter generation,
vs: the welding voltage at the moment of spatter generation,
the units of Vs and Va are V.
4. A method for manufacturing a resistance spot welding joint using the resistance spot welding method according to any one of claims 1 to 3.
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| JP2019-176780 | 2019-09-27 | ||
| JP2019176780 | 2019-09-27 | ||
| PCT/JP2020/028615 WO2021059720A1 (en) | 2019-09-27 | 2020-07-27 | Resistance spot welding method and method of manufacturing resistance spot welded joint |
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| CN114466721B true CN114466721B (en) | 2024-03-22 |
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| US (1) | US20220339731A1 (en) |
| EP (1) | EP3995246A4 (en) |
| JP (1) | JP7296985B2 (en) |
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| CN105358284A (en) * | 2013-07-11 | 2016-02-24 | 新日铁住金株式会社 | Resistive spot welding method |
| CN105792977A (en) * | 2013-12-05 | 2016-07-20 | 杰富意钢铁株式会社 | Resistance-spot-welding method |
| CN107530818A (en) * | 2015-04-27 | 2018-01-02 | 杰富意钢铁株式会社 | Resistance spot welding method |
| CN108136534A (en) * | 2015-10-21 | 2018-06-08 | 新日铁住金株式会社 | Resistance spot welding method |
| JP2019072764A (en) * | 2017-10-16 | 2019-05-16 | Ｊｆｅスチール株式会社 | Resistance spot weld method and manufacturing method of resistance spot weld member |
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| ES2657122T3 (en) | 2013-04-17 | 2018-03-01 | Nippon Steel & Sumitomo Metal Corporation | Spot welding method |
| JP6194765B2 (en) | 2013-11-08 | 2017-09-13 | 新日鐵住金株式会社 | Spot welding method for high strength steel sheet |
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- 2020-07-27 JP JP2020558057A patent/JP7296985B2/en active Active
- 2020-07-27 US US17/762,486 patent/US20220339731A1/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105358284A (en) * | 2013-07-11 | 2016-02-24 | 新日铁住金株式会社 | Resistive spot welding method |
| CN105792977A (en) * | 2013-12-05 | 2016-07-20 | 杰富意钢铁株式会社 | Resistance-spot-welding method |
| CN107530818A (en) * | 2015-04-27 | 2018-01-02 | 杰富意钢铁株式会社 | Resistance spot welding method |
| CN108136534A (en) * | 2015-10-21 | 2018-06-08 | 新日铁住金株式会社 | Resistance spot welding method |
| JP2019072764A (en) * | 2017-10-16 | 2019-05-16 | Ｊｆｅスチール株式会社 | Resistance spot weld method and manufacturing method of resistance spot weld member |
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| JP7296985B2 (en) | 2023-06-23 |
| WO2021059720A1 (en) | 2021-04-01 |
| CN114466721A (en) | 2022-05-10 |
| MX2022003474A (en) | 2022-04-19 |
| JPWO2021059720A1 (en) | 2021-10-07 |
| KR20220047647A (en) | 2022-04-18 |
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| EP3995246A4 (en) | 2022-09-14 |
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